Alpha subunit of glycoprotein hormone: presence in peripheral serum after LHRH

A method is described for the selective measurement of human luteinizing hormone (hLH) and alpha subunit. The assays employ highly purified tracers of hLH and of subunit of human chorionic gonadotropin (hCGalpha) and a "mixed population" of antibody: Population I (directed against determinants on beta subunit of hCG) and Population II (directed against determinants on alpha subunit of hCG). The former is present in greater concentration than the latter. When the mixed antibody is used at higher dilution (1:1.2x10(6)), Population II is effectively diluted out, and using 125I-labelled hLH as tracer, the assay recognize hLH, hCG and their beta subunits 20-50 times more sensitively than hCGalpha. When the mixed antibody is used at fivefold higher concentration, Population I is present in relative excess and acts as a "sink" for hCG, hLH and their beta subunits. Under these conditions, using 125I-hCGalpha as tracer, the assay recognize the alpha subunit 20 to 50-fold more sensitively than hLH and hCG. These assays have been employed in the study of sera which have been filtered over Sephadex G-100. Alpha subunit was detected in serum within minutes after intravenous injection of luteinizing hormone releasing hormone (LHRH) in four subjects tested.